Dietary Plant Polyphenols: Effects of Food Processing on Their Content and Bioavailability

molecules Review Dietary Plant Polyphenols: Effects of Food Processing on Their Content and Bioavailability Leila Arfaoui Department of Clinical Nutrition, Faculty of Applied Medical Sciences, King Abdulaziz University, P.O. Box 80324, Jeddah 21589, Saudi Arabia; [email protected]; Tel.: +966-0126401000 (ext. 41612) Abstract: Dietary plant polyphenols are natural bioactive compounds that are increasingly attracting the attention of food scientists and nutritionists because of their nutraceutical properties. In fact, many studies have shown that polyphenol-rich diets have protective effects against most chronic diseases. However, these health benefits are strongly related to both polyphenol content and bioavailability, which in turn depend on their origin, food matrix, processing, digestion, and cellular metabolism. Although most fruits and vegetables are valuable sources of polyphenols, they are not usually consumed raw. Instead, they go through some processing steps, either industrially or domestically (e.g., cooling, heating, drying, fermentation, etc.), that affect their content, bioaccessibility, and bioavailability. This review summarizes the status of knowledge on the possible (positive or negative) effects of commonly used food-processing techniques on phenolic compound content and bioavailability in fruits and vegetables. These effects depend on the plant type and applied processing parameters (type, duration, media, and intensity). This review attempts to shed light on the importance of more comprehensive dietary guidelines that consider the recommendations of processing parameters to take full advantage of phenolic compounds toward healthier foods. Citation: Arfaoui, L. Dietary Plant Keywords: plant polyphenols; food processing; phenolic content; bioavailability; bioaccessibility Polyphenols: Effects of Food Processing on Their Content and Bioavailability. Molecules 2021, 26, 2959. https://doi.org/10.3390/ 1. Introduction molecules26102959 Recent progress in nutrition and medicine has metamorphosed the way healthcare is conceived and delivered. An international technology-driven revolution is driving this Academic Editors: Jan Oszmianski rapid change from traditional healthcare to precision medicine by establishing unprece- and Sabina Lachowicz dented research programs and networks that prioritize diseases’ prevention and health promotion mainly through lifestyle and diet-based approaches [1]. A recent emerging area Received: 16 April 2021 of precision nutrition focusing on bioavailable and metabolizable proportions of ingested Accepted: 14 May 2021 Published: 16 May 2021 foods with claimed health benefits has been developed. In this context, plant-derived polyphenols have been associated with several health benefits and are considered bioactive Publisher’s Note: MDPI stays neutral dietary compounds [2]. Polyphenols are the largest group of dietary antioxidants known with regard to jurisdictional claims in for their ability to scavenge free radicals, donate hydrogen atoms, electrons, or chelate published maps and institutional affil- metal cations [3]. Because of these mechanisms, they have protective and preventive effects iations. against several non-communicable diseases (NCDs), including cardiovascular diseases (CVDs), cancer, and diabetes [4]. However, the health implications of dietary polyphenols are determined by their bioavailability to a great extent, which is defined as the fraction of polyphenols released from the food matrix, metabolized, absorbed, and able to impose its bioactivity on the Copyright: © 2021 by the author. Licensee MDPI, Basel, Switzerland. target cells or tissues [5]. Several factors influence polyphenol bioavailability, including the This article is an open access article initial content in foods, food matrix, gut microbiota, and food processing [6]. In fact, most distributed under the terms and fruits and vegetables are not usually consumed raw. Instead, they go through industrial conditions of the Creative Commons or domestic processing steps (e.g., cooling, heating, drying, fermentation, etc.) that affect Attribution (CC BY) license (https:// their content, bioaccessibility, and bioavailability. creativecommons.org/licenses/by/ The main purpose of food-processing techniques is to transform raw ingredients into 4.0/). food, or to transform food into other end-products suitable for human or animal consump- Molecules 2021, 26, 2959. https://doi.org/10.3390/molecules26102959 https://www.mdpi.com/journal/molecules Molecules 2021, 26, 2959 2 of 35 tion. Some specific objectives include extending the shelf life of ingredients and products by inactivating pathogens or contaminating microorganisms, enhancing the bioavailability of otherwise inaccessible nutrients, enabling variety in flavor, texture, or aroma of certain foods, and improving the nutrient profile [7]. Domestic and industrial processing affect phenolic compounds’ content, antioxidant capacity, bioaccessibility, and bioavailability in different ways. While many food-processing techniques may lead to phenolic compounds’ degradation, some others enhance their absorption and bioavailability [8,9]. The final polyphenol content and bioavailability in processed food depend, therefore, on factors such as the nature of the process, duration of treatment, and food matrix subjected to the processing technique [10]. Since dietary polyphenol consumption has been increasingly proposed as an effective measure in the primary prevention and management of NCDs, it is imperative to consider the effect of food processing on their content and bioavailability. This review aims to summarize the effects of the most common food-processing techniques, either domestic or industrial, on dietary polyphenol content, bioaccessibility, and bioavailability. To introduce the topic, a glance at polyphenol types, sources, health implications, and the concepts of bioavailability and bioaccessibility is provided. 2. Polyphenol Types and Sources The largest antioxidant group present in the human diet is that of phenolic compounds, with more than 8000 different structures identified to date [11]. Plants produce these secondary metabolites in response to ultraviolet light or pathogen attacks [12]. The molecular structure is based on one or several aromatic rings and at least one hydroxyl (phenol) group. They can either have a simple structure (such as in the case of phenolic acids) or a complex structure (such as in the case of flavonoids). Based on their molecular structure, phenolics are divided into five main groups: phenolic acids, flavonoids, stilbenes, coumarins, and tannins [9]. As phenolic acids and flavonoids were mostly investigated in studies reporting the association between food processing and polyphenol content and bioavailability, these two classes are discussed in greater detail. 2.1. Phenolic Acids Phenolic acids are non-flavonoid polyphenols, and their typical representatives are hydroxybenzoic acids (e.g., gallic, p-hydroxybenzoic, vanillic, and syringic acids) and hy- droxycinnamic acids (e.g., ferulic, caffeic, p-coumaric, chlorogenic, and sinapic acids). They exist in bound or free form in fruits and vegetables. Grains and seeds are particularly rich in bound phenolic acids, which are released after acid or alkaline hydrolysis or enzymatic reactions [11]. Good sources of phenolic acids are fruits (apples, cherries, berries, and their products, such as wine), vegetables (broccoli, lettuce, and tomatoes), legumes, cereals, and coffee beans [13]. 2.2. Flavonoids Flavonoids are a large group of polyphenols that typically contain two aromatic rings linked by a heterocycle. Their subclasses are distinguished by structural differences based on this heterocycle [14]. These subgroups include anthocyanins, flavan-3-ols, flavones, flavanones, and flavonols [11]. Flavones, flavonols, and flavanones are widely distributed in plants. Flavones and their derivatives flavonols, as well as their acylated products, represent the largest polyphenol subgroup [15]. Quercetin and kaempferol are, for example, the most commonly found flavonol aglycones, and they alone have approximately 300 different glycosidic combinations [15]. The most relevant flavone sources are citrus fruits, parsley, lettuce, and grapes, while flavanones are mostly present in citruses and products based on them [13]. Among all flavanones, hesperidin and naringenin are typical representatives. Good dietary sources Molecules 2021, 26, x FOR PEER REVIEW 3 of 34 Flavones, flavonols, and flavanones are widely distributed in plants. Flavones and their derivatives flavonols, as well as their acylated products, represent the largest polyphenol subgroup [15]. Quercetin and kaempferol are, for example, the most commonly found flavonol aglycones, and they alone have approximately 300 different glycosidic combinations [15]. The most relevant flavone sources are citrus fruits, parsley, Molecules 2021, 26, 2959 lettuce, and grapes, while flavanones are mostly present in citruses and products 3based of 35 on them [13]. Among all flavanones, hesperidin and naringenin are typical representatives. Good dietary sources of flavonols include plums, apples, onions, and blueberries, with kaempferol and quercetin being the main representatives [13]. of flavonolsFlavanols include are plums,a very apples,complex onions, group and of blueberries, polyphenols, with which kaempferol include and compounds quercetin beingranging the mainfrom representatives monomeric [ 13].flavan-3-ols to polymeric proanthocyanidins. ProanthocyanidinsFlavanols

Load more